Gravimetric measuring instruments of this kind, for example in the form of balances and weighing modules, are used in many industrial applications, particularly in laboratories of research- and development departments, but also as weighing modules in production departments, for example in quality control. Weighing modules are balances whose result display and/or input unit is arranged in separation from the weighing cell and its enclosure housing.
A weighing module with a weighing cell is illustrated schematically in cross-section in EP 1 576 343 B1. The load-transmitting member which is arranged at the load-receiving portion of the weighing cell has a free end of frusto-conical shape. The load receiver shown in the drawing has a conically tapered hole that conforms to the frusto-conical free end. The truncated cones in this kind of releasable connection usually have a small conical taper angle, so that even with an eccentrically placed load on the load receiver, the latter cannot tip over and fall off the load-transmitting member. Due to the small conical taper angle, the inside wall of the hole is subjected to extremely high surface forces, i.e., to a large amount of contact pressure. This type of connection is therefore only suitable for balances with small maximum load capacities, even if the connection is made of metal. Furthermore, this type of connection can only be used in cases where the orientation of the load receiver relative to the weighing cell is irrelevant irrespective of the location of the mass center of gravity of the load receiver. Consequently, this type of connection can only be used in cases where the load receivers or weighing pans are rotationally symmetric.
Due to the aforementioned reasons, this kind of connection is in most cases unsuitable for weighing modules in industrial applications. Normally, the load receiver is therefore fastened to the load-transmitting member directly by means of a screw thread. This has the disadvantage that the installation and removal of the load receiver takes a considerable amount of time, since the entire load receiver has to be rotated in relation to the weighing cell. This causes problems in particular if accessory devices for specific applications, such as for example conveyor belts, clamping fixtures for containers and the like are fastened to the load receiver and if the spatial constraints are so tight that these accessory devices first have to be removed from the load receiver before the latter can be unscrewed from the load-transmitting member. Weighing modules with accessory devices for specific applications are often employed in filling- and checking devices of production lines for the portioning and checking of bulk materials. Such production lines often have a multi-lane layout, which means that a plurality of parallel weighing modules as well as their infeed and outfeed devices are packed into a very compact space.
According to another state-of-the-art design concept, the load receiver or weighing pan is fastened to the load-transmitting member by means of a screw which is arranged along the central lengthwise axis of the load receiver and the load-transmitting member. While this makes it easier to remove the load receiver from the load-transmitting member without having to turn the entire load receiver, the hole for the screw creates a possible leakage path through the load receiver which needs to be sealed. In many cases, screw connections of this type are highly undesirable for sanitary reasons and ease of cleaning, as the screw is arranged in a horizontal surface and contaminants can accumulate around the screw head. Obviously, especially where such production lines have to meet the highest standards of cleanliness, for example in the food and pharmaceutical industries, a quick way of installing and removing the load receiver for the purpose of cleaning the latter is absolutely essential. In addition, it is a normal design requirement for weighing modules that are used in these production facilities that the accessory devices for specific applications must be adapted to the product being weighed and also have to be designed for interchangeability. A design with a screw arranged along the central lengthwise axis of the load receiver and the load-transmitting member is clearly unsuitable, as the screw is covered up by the accessory device.
Another concept for mounting the load receiver is disclosed in EP 2 278 285 A1, which circumvents the aforementioned issue with the screw along the central lengthwise axis of the load receiver and the load-transmitting member. A stop of the load-transmitting member can be pushed tightly against a counter stop of the load receiver by an eccentric bolt acting on the load receiver and on the load-transmitting member, whereby the stop is held under a pre-tensioning force against the counter stop. Instead of requiring multiple turns of a screw or of the entire load receiver, the latter can be rigidly fastened to the load-transmitting member by simply setting the load receiver onto the load-transmitting member and by inserting and turning an eccentric bolt. This concept has the disadvantage that in order to separate the load receiver from the load-transmitting member, the eccentric bolt has to be released and taken out first and that a sufficient amount of space has to be available for the release and removal of the eccentric bolt. This applies likewise to a tool that may be used for this operation.
It is therefore the object of the present invention to provide a gravimetric measuring instrument with a weighing cell designed so that a load receiver can be quickly attached to and released from the load-transmitting member of the weighing cell, wherein the space required for the installation and removal of the load receiver is kept to a minimum.